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BIOMECHANICS CHAPTER 15 IN TEXTBOOK INTRODUCTION • Biomechanics: the application of mechanical principles in the study of living organisms. • Bio: structure and function of living organisms • Mechanics: analysis of the actions of forces SUB-BRANCHES OF BIOMECHANICS • Statics: study of systems in constant motion, including systems at rest (zero motion). • Dynamics: study of systems that are subject to acceleration. • Kinematics: study of the description of motion (space and time). • Kinetics: study of the actions of forces (“push” or “pull”) acting on systems. SYSTEM • A system is any structure or organization of related structures whose state of motion is of analytical interest. • A system of interest should be selected BEFORE deciding to how best to analyze motion. • A system could be: • An entire human (e.g, treat the whole body as a “point” during a jump) • Part of human (e.g., throwing arm, knee joint when walking) • An object the human has struck or manipulated (e.g., soccer ball, barbell during a clean-and-jerk) NEWTON’S MODELS • Sir Isaac Newton created this model in 1687. • Known as the Three Laws of Motion • Explain how forces work and became the basis for modern physics and thus biomechanical aswell 1. Law of Inertia 2. Law of Acceleration 3. Law of Reaction LAW OF INERTIA • A body will maintain a state of rest or constant velocity unless acted on by an external force that changes the state. • Therefore, a motionless object will remain motionless unless there is a net force (not counteracted by another force) acting on it. • Similarly, a body travelling with a constant speed along a straight path will continue its motion unless acted on by a net force that alters its SPEED or DIRECTION of motion. • What external forces can be applied to the body when standing still? What does it depend on? LAW OF ACCELERATION • Is an expression of the interrelationships among force, mass and acceleration. F=ma (force = mass x acceleration) • A force applied to a body causes an acceleration of that body of a magnitude proportional to the force, in the direction of the force, and inversely proportional to the body’s mass. NEWTONS • Force is measured in Newtons (N) • 1N = 1 (kg) (m) / (s2) • Gravity is a pulling force which is exerted on us by the earth and it occurs at a rate of 9.8 m/s2 • Thus, something that is 102 grams or 0.102 kg would have a weight of 1 N on earth. ( 0.102 x 9.8 = 1N) • ***1000 grams = 1kg MECHANICAL LOADS ON THE BODY • Stress is the distribution of force within a body. Quantified as force divided by the area over which the forces act. • Types of stress: • Axial- directed along the longitudinal axis of a body • Compression- pressing of squeezing force directed axially through a body • Tension- pulling or stretching force directed axially through a body • Shear- force directed parallel to a surface. • Bending- asymmetric loading that produces tension on one side of a body’s longitudinal axis and compression on the other side. • Torsion- load producing twisting of a body around its longitudinal axis • Combined- simultaneous action of more than one of the pure forms of loading. WEIGHT VS MASS • Weight and Mass are not the same! • Mass: Quantity of matter comprising an object. Measured in kilograms [kg] • Weight: amount of gravitational force exerted on an object. Product of mass (m) and gravitational acceleration (g) wt= mg [N]. • Since weight is a force, in addition to its magnitude[N], its point of application and direction must be specified. • Direction is toward center of the earth. • Point of application is CoG. FORMS OF MOTION • Linear motion (translation) • Rectilinear (motion along a straight line) • Curvilinear (motion along a curved line) • Angular motion (rotation) • Rotation around a fixed axis (circular path) • General motion • Combination of linear and angular motion http://www.youtube.com/watch?v=MNDB5QU5bB Y ANGULAR MOTION • Just like Mass this is the resistance to rotation/movement. The larger the moment of inertia the larger the moment of force required to spin or stop spinning. In other words, the further the mass is from the axis, the greater the moment of inertia and thus the harder it is to start or stop spinning and vice versa. • Figure skater pg 229. As the skater brings their arms into the centre of their body their angular acceleration increases because they have reduced their moment of inertia. • Gymnastics---following a series of rapid somersaults in mid air the athlete straitens out their body. By opening up they increase their moment of inertia and slow down as they prepare to land. (i,e. the force stays the same and there is now a larger moment of force thus the body slows down LAW OF REACTION • For every action, there is an equal and opposite reaction. • When one body exerts a force on a second, the second body exerts a reaction force that is equal in magnitude and the opposite in the direction on the first body. Sample problem: A 90 kg ice hockey player collides head-on with an 80 kg player. If the first player exerts a force of 450 N on the second player, how much force is exerted by the second player on the first? TYPES OF FORCES • Internal forces- e.g. muscles pulling on bones • External forces- e.g. gravity, contact with ground, environment (wind), sport equipment, opponent, etc. SEVEN PRINCIPLES OF BIOMECHANICS • Grouped into four categories: • • • • Stability Maximum effort Linear Motion Angular Motion STABILITY • “Proper stability & balance are essential to efficient movement” • Resistance to disruption of equilibruim • See notes on stability from earlier unit. MAXIMUM EFFORT – PRINCIPLE 2 • “Production of maximum force requires the use of all possible joint movements that contribute to the task’s objective.” • With more joints coming into play, the more muscles there will be to contract – leading to greater force being exerted. MAX EFFORT- PRINCIPLE 3 • “Production of maximum velocity requires the use of joints/muscles in order – from largest to smallest.” LINEAR MOTION- PRINCIPLE 4 • “The greater the applied impulse or force, the greater the increase in velocity.” • The harder you hit an object, the farther it will travel. • Impulse: product of force and the time over which the force acts (J). The product of force (F) and time (t) J=Ft [Nxs] • When a vertical jump is executed, the larger the impulse generated against the floor, the greater the jumper’s takeoff velocity and the higher the resulting jump. • Impulse can be positive or negative. WHY? LINEAR MOTION- PRINCIPLE 5 • “Movement usually occurs in the direction opposite that of the applied force.” • Examples: Resistance of water in swimming, pushing off floor before jumping, etc. • Related to Newton’s 3rd Law (Reaction) ANGULAR MOTION- PRINCIPLE 6 • “Angular motion is produced by the application of a force acting at some distance from an axis.” • Angular velocity increases closer the object is to the axis of rotation. • Examples: figure skating spinning, diver spinning, throwing a curve ball. ANGULAR MOTION- PRINCIPLE 7 • “Angular momentum is constant when an athlete or object is free in the air (or airborne).” SCALARS VS. VECTORS • Scalar quantities: Quantitiy described by magnitude ALONE. • E.g., speed, distance, mass, length, energy, volume, density • Vector quantities: Quantity possessing magnitude AND direction, and adds according to the parallelogram law. • E.g., force, moment of force (torque), displacement, velocity, acceleration, momentum. VECTOR OPERATIONS • Vector composition: Two of more vectors can be ADDED to produce a single vector quanitity called a “resultant” (adding) • Vector Resolution: Vectors can be resolved into their perpendicular components (subtracting) • Vector composition and resolution can be performed: • Graphically: represent vectors as arrows • Trigonometrically: Use basic trigonometric relationships (solving right angle problems using SohCahToa) VECTOR COMPOSITION- GRAPHICALLY Tip to tail Make a triangle VECTOR OPERATIONSTRIOGOMETRICALLY • Resolve vectors V1 and V2 into their rectangular components and find the resultant (Vr=V1+V2) MUSCLE FIBER ARCHITECTURE • An important variable influencing muscle function is the arrangement of fibers within a muscle. These structural considerations affect the strength of muscular contraction and the range of motion through with a muscle group can move a body segment. • Two categories of muscle fiber arrangements are termed parallel and pennate. Parallel- the fibers are oriented largely in parallel with the longitudinal axis of the muscle. (e.g., sartorius, rectus abdominis, and biceps brachii) Pennate- the fibers lie at an angle to the muscle’s longitudinal axis. Each fiber in a pennate muscle attaches to one or more tendons, some of which extend the entire length of the muscle. The fibers of a muscle may exhibit more than one angle of pennation (angle of attachment) to a tendon. The tibialis posterior, rectus femoris, and deltoid are pennated muscles PHYSICAL FITNESS PART 3 OF BIOMECHANICS PHYSICAL FITNESS • The body’s ability to function efficiently, to enjoy leisure time, and be healthy, and resist hypokinetic diseases • Consists of health related fitness and skill related fitness Health related Body composition Cardiorespiratory capacity Flexibility Muscular endurance Muscular strength Skill related Agility Balance Coordination Power Reaction time Speed BODY COMPOSITION • Relative percentage of muscle, fat, bone • A person who is physically fit has a relatively high amount of lean muscle mass, and bone density • Body fat for men 5-25% • Body fat for women 830% CARDIO-RESPIRATORY FITNESS The ability of the heart, lungs and blood vessels to deliver oxygen, and nutrients efficiently to the tissues Individuals who are Physically fit, have higher ventilitory thresholds and anaerobic thresholds FLEXIBILITY • Range of motion available in a specific joint. • This becomes problematic later on in life as it limits an individual’s range of motion and thus ability to perform every day functions. MUSCULAR ENDURANCE Ability of a muscle to repeatedly exert itself A fit person can repeat movements over a longer period of time How many times? • The ability to exert an external force or lift/move a heavy object. • Can hinder an individual’s ability to complete daily chores/activities • How much? AGILITY • Ability to rapidly and accurately change direction of the entire body in space. BALANCE • Static Balance- ability to maintain equilibrium while stationary • Dynamic Balanceability to maintain equilibrium while moving COORDINATION • Ability to use senses with the body to perform motor tasks smoothly and accurately SPEED • The ability to perform a movement in a short period of time. POWER • The ability to exert a force at a fast rate • This is the combination of muscular strength and speed REACTION TIME • The time elapsed between the stimulus/stimulation and the beginning to the reaction to the stimulus TRAINING • Sir Roger Bannister became the first person to run a mile in less than 4 minutes (1954) • His training techniques were at the cutting edge in that day…. • However if you were to compare them to today’s methods they seem quite primitive WHAT IS TRAINING It is a process by which the human body is made more efficient. In physical activity, individuals seek to improve their fitness components through training Eg. Running longer/faster, shooting a basketball more accurately, or lifting more weight It is a process by which the human body is made more efficient. In physical activity, individuals seek to improve their fitness components through training Eg. Running longer/faster, shooting a basketball more accurately, or lifting more weight F.I.T.T • Common training program • Frequency: providing just enough stress for the body to adapt to AND allowing enough tme for healing and adaptation to occur. • Intensity: the amount of effort that should be invested in the training program or one session. (measure by THR & MHR) • Type: what type or kind of exercise you should choose to achieve the appropriate training response • Time: how long you SHOULD be exercising for. F.I.T.T TRAINING PRINCIPLES • Overload • Progression • Specificity • Individual Differences • Reversibility • Diminishing Returns TRAINING PRINCIPLES • Overload: In order for physiological change to occur, the human body must be subjected to greater stresses than it is accustomed to. Applies to aerobic and anaerobic exercise. • Eg. Of aerobic overload? • Eg. Of anaerobic overload? • Progression: In order for the effect of the training to progress, the athlete must be subjected to progressively greater and greater overloads. • Eg. Once you can lift 100 lbs on the bench press 12 times on your 3rd set increase the amount to 110 lbs. TRAINING PRINCIPLES • Specificity: Also called the S.A.I.D. principle ( Specific Adaptations to Imposed Demand). In order for specific outcomes to occur, training exercises must be specific to those outcomes. Thus the training should mimic activities from the actual sport. • Individual Differences: Every athlete has a different physiological and psychological makeup and thus will have different needs when training. • E.g. History, type of activity, fitness level, age, gender, ability to recover from intense workouts. • Reversibility: When training is removed, muscles will over time lose the benefits that training brought about. Atrophy occurs, and muscles lose size and strength. Use it or lose it! • Diminishing Returns: Individuals who have trained little or not at all will experience greater results than those who have trained for longer periods of time. • Elite Sprinters train endlessly in hopes of decreasing their times by hundredths of seconds while a beginner may decrease their time by seconds • Plateaus often occur in individuals training for long periods of time